190 STECKBECK— ON COMPARATIVE HISTOLOGY 



and the pulvinus previously of a whitish hue assumes a dull greenish 

 aspect. This color change is due to migration of liquid into the upper 

 region of the pulvinus." 



Cunningham (10) fully described the pulvini of various sensitives — 

 mainly Mimosa pudica — as motor organs. He states "The idea is 

 erroneous, that in the opposing masses of tissue in pulvini, we have to 

 deal with differences depending solely on invisible molecular structure, 

 and not on the presence of any visible difference in organization. 



Haberlandt (19) considered that the epidermal hairs found on sen- 

 sitive plants especially those on the pulvini of Mimosa and the leaflets 

 of Biophytum are receptors of stimuli. Experiments are given in support 

 of this view. Shortly before Haberlandt's paper, Renner (39) had 

 emphasized the presence of various kinds of hairs on sensitives. 



The different works of Bose (5) that have appeared during recent 

 years have added much to our knowledge of Plant Irritability. By 

 means of very ingenious devices he has recorded accurately the various 

 movements of some of the sensitive plants, especially Mimosa pudica 

 and Desmodium gyrans. 



Recently Linsbauer (25) made observations on propagation of stimuli 

 in Mimosa pudica. He writes that propagation of wound stimuli 

 (traumatic) can take place for considerable distances in the stem, even 

 if all of the tissue outside of the wood is removed. He denies the pre- 

 sence of special conducting elements in the phloem. 



The above brief historical review includes only some of the more 

 important references on irritability. Other references will be quoted 

 in the body of this work. 



Distribution and Relative Sensitivity 



Leguminosae 



This family is very widely distributed in both hemispheres, from 

 the cold, almost frigid, regions to the tropics, where a large number of 

 genera grow in great profusion. 



In the colder temperate regions, only a few members are found that 

 are sensitive to any degree, and such sensitiveness is shown only in 

 response to light stimulation, that is to nyctitropic stimuli and to the 

 effects of rather intense sunlight. There is no response, or a very slight 

 response, to other kinds of stimuli, such as mechanical, chemical, ther- 

 mic, electric and other forms. Species of Lathyrus, Vicia and Amorpha 

 extend northward to the Arctic Circle. The northern limit of some 



